This proposal is concerned with the conversion of "non-lemniscal" afferent input into thalamocortical relay cell output in the ventrobasal (VB) nuclei of the cat thalamus. Such mechanisms may form a fundamental basis for the sensory discriminative aspects of pain, and as such, become important in future studies concerning pain relief in both te normal and pathologic states. The specific aims are: (1) determine the morphological characteristics of the terminal arborizations of individual spinothalamic (STT) and cervicothalamic (CTT) tract axons in VB, (2) determine the relationships of STT and CTT axon terminals to thalamcortical relay and intrinsic neurons in VB, (3) examine the morophological characteristics and exact synaptic patterns of individual, functionally identified and intra-axonally labeled STT and CTT terminal arbors in VB, (4) correlate differences in the synaptic patterns of non-lemnisal and lemniscal afferents with differences in their functional properties. Three primary sets of experiments are to be conducted at both light and electron microscopic levels: (a) a morphological analysis of the branching and termination patterns of anterogradely labeled STT and CTT axons in VB, (b) a study combining the morphological analysis of anterogradely labeled STT and CTT axon terminations with the characterization of their postsynaptic targets in VB, and (c) a physiological study of individually identified STT and CTT fibers utilizing intraxonal labeling techniques to establish structure/function relationships of non- lemniscal afferent fibers in VB.